The invention concerns a safety retainer for threaded or rapid couplings used to create a connection between a pressurized system in combination with a male tube connector nipple cooperating with a female bore in a fixed receiving nipple or bush and a sealing ring arranged in an expanded part of the bore in the receiving bush applied against the mating connecting male nipple, together with a check valve, opening upon contact from the outside and located in the coupling bush.
Threaded couplings of this type serve, for example, to establish testing or measuring connections on pressurized lines, with the coupling bush securely and usually fixedly installed, usually with external threading, on the pressure line of hydraulic or pneumatic systems. For the duration of the testing or measuring work, a sealing connector nipple including a hollow male pin is screwed into the coupling bush by means of a cap nut, solidly connected with a flexible tube or pipe. The couplings may be connected, for example, under pressure, i.e. without closing down the installation, with suitable measuring instruments by means of measruing tubes.
With permanently installed instruments, for example manometers, manometer selector switches and pressure switches, the flexible measuring tubes may be connected in the manner of electric cables so that the expensive installation of tubing is eliminated. With such measuring couplings, therefore, effective working pressures can be measured directly on hydraulic instruments without having to loosen vent screws and threaded tube connections. Couplings of this type are used in various structural elements and controls of hydraulic or pneumatic systems.
Following the disconnection of the coupling connection, a protective cap is screwed onto the coupling bush with its external thread for the purpose of preventing the entrance of dirt into the coupling bush and to provide an additional sealing function in the event that the check valve installed in the coupling bush should fail to seal tightly.
A prestressed elastic ring, known per se, performs a sealing function and secures the cap device against turning. The prestressing of the sealing and antiturning ring usually cannot exceed a certain very slight degree, because otherwise the introduction of a male cylindrical tube nipple, slotted in keeping with the present state of the art, would cause the immediate destruction of the ring.
The protective caps and tube connection and coupling bushes, known in themselves, are provided with standard threading and can be screwed together with the exertion of great care only, so that the protective cap or tube connection is screwed on until their internal contact surface touches the end surface of the fixed coupling bush. Additional torque must then be applied in order to securely tighten the protective cap or tube connection and, because for reasons of safety and convenient handling they are equipped with knurling only, the torque must be applied by hand. For this reason it is not immediately possible to determine the reliability of the connection, because it depends very substantially on the conscientiousness and force of the person who performs the screwing on of the protective cap or tube connection.
In cases where the pressure lines with the coupling parts installed are exposed to strong mechanical vibrations, even adequately tightened protective caps and tube connections may loosen by themselves, resulting in the loss of protection against dirt or in measuring errors with substantial subsequent potential damage. This occurs specifically because both the standard thread and the sealing and antiturning ring, the latter only slightly prestressed for wear considerations, are incapable of providing extensive resistance against the loosening of the protective cap or cap nut. This is a great disadvantage particularly when the hydraulic or pneumatic installation is used in very dirty environments, for example in dirty rooms or on the hydraulic lines of construction machinery or trucks.
Substantial danger may develop, if, for example, permanently installed measuring instruments provide false signals because of loose tube connections, leading to failures or incorrect control signals.
Another disadvantage of the prior art couplings consists of the fact that particularly the sealing and antirotation ring is subject to extensive wear, for reasons of design, and even under slight prestressing, especially if the decoupling process takes place under high pressures. Because the pressure in the connecting space between the coupling connector and the instrument connected is not released immediately, due to the retention of pressure following the closing of the check valve, the sealing and antirotation ring tends to migrate outwardly when the notched hollow pin of the tube connected sealing nipple is pulled out and to become squeezed in the slit between the internal surface of the extended part of the bush bore and the external surface of the hollow pin, particularly in its notched area.